An approach to evaluate immune function consisting of T cell proliferative responses to mitogens and recall antigens as well as B cell responses to recall and neo antigens has been developed. It is now operational and is providing critical information in the evaluation of patients with possible immune disorders and in following patients post bone marrow transplantation. This has been supplemented with additional testing to evaluate the T cell antigen receptor repertoire using TcR spectratyping with 26 pairs of PCR primers directed at the 24 major families of TcR beta chains. These studies are being used in assessing patients with congenital immune deficiency disorders and evaluating these patients post cellular reconstitution.. In addition, T cell receptor excision circle (TREC) assessment has also been developed to assess post bone marrow transplant patients thymic output and to be applied to immune deficient patients undergoing gene therapy in the future.